linux-kernel - Re: [PATCH v2 2/4] mfd: cros_ec: add EC

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Message-ID: <20160617192133.GA83919@google.com>
Date:	Fri, 17 Jun 2016 12:21:33 -0700
From:	Brian Norris <briannorris@...omium.org>
To:	Lee Jones <lee.jones@...aro.org>
Cc:	Thierry Reding <thierry.reding@...il.com>,
	Olof Johansson <olof@...om.net>, linux-kernel@...r.kernel.org,
	Doug Anderson <dianders@...omium.org>,
	Brian Norris <computersforpeace@...il.com>,
	linux-pwm@...r.kernel.org, devicetree@...r.kernel.org,
	Boris Brezillon <boris.brezillon@...e-electrons.com>,
	Stephen Barber <smbarber@...omium.org>,
	Javier Martinez Canillas <javier@....samsung.com>,
	Benson Leung <bleung@...omium.org>,
	Enric Balletbo <enric.balletbo@...labora.co.uk>,
	Randall Spangler <rspangler@...omium.org>,
	Shawn Nematbakhsh <shawnn@...omium.org>,
	Dmitry Torokhov <dmitry.torokhov@...il.com>,
	Todd Broch <tbroch@...omium.org>,
	Gwendal Grignou <gwendal@...omium.org>,
	Tomeu Vizoso <tomeu.vizoso@...labora.com>
Subject: Re: [PATCH v2 2/4] mfd: cros_ec: add EC_PWM function definitions

On Thu, Jun 16, 2016 at 04:38:17PM +0100, Lee Jones wrote:
> On Thu, 02 Jun 2016, Brian Norris wrote:
> > The EC_CMD_PWM_{GET,SET}_DUTY commands allow us to control a PWM that is
> > attached to the EC, rather than the main host SoC. The API provides
> > functionality-based (e.g., keyboard light, backlight) or index-based
> > addressing of the PWM(s). Duty cycles are represented by a 16-bit value,
> > where 0 maps to 0% duty cycle and U16_MAX maps to 100%. The period
> > cannot be controlled.
> > 
> > This command set is more generic than, e.g.,
> > EC_CMD_PWM_{GET,SET}_KEYBOARD_BACKLIGHT and could possibly used to
> > replace it on future products.
> > 
> > Let's update the command header to include the definitions.
> > 
> > Signed-off-by: Brian Norris <briannorris@...omium.org>
> > ---
> > v2: no change
> > 
> >  include/linux/mfd/cros_ec_commands.h | 31 +++++++++++++++++++++++++++++++
> >  1 file changed, 31 insertions(+)
> > 
> > diff --git a/include/linux/mfd/cros_ec_commands.h b/include/linux/mfd/cros_ec_commands.h
> > index 13b630c10d4c..d673575e0ada 100644
> > --- a/include/linux/mfd/cros_ec_commands.h
> > +++ b/include/linux/mfd/cros_ec_commands.h
> > @@ -949,6 +949,37 @@ struct ec_params_pwm_set_fan_duty {
> >  	uint32_t percent;
> >  } __packed;
> >  
> > +#define EC_CMD_PWM_SET_DUTY 0x25
> > +/* 16 bit duty cycle, 65535 = 100% */
> > +#define EC_PWM_MAX_DUTY 65535
> 
> Any reason this isn't represented in hex, like we do normally?

Hex would probably be clearer. I'll try to change that.

> > +enum ec_pwm_type {
> > +	/* All types, indexed by board-specific enum pwm_channel */
> > +	EC_PWM_TYPE_GENERIC = 0,
> > +	/* Keyboard backlight */
> > +	EC_PWM_TYPE_KB_LIGHT,
> > +	/* Display backlight */
> > +	EC_PWM_TYPE_DISPLAY_LIGHT,
> > +	EC_PWM_TYPE_COUNT,
> > +};
> 
> Are these comments really necessary?  I'd recommend that if your
> defines require comments, then they are not adequately named.  In this
> case however, I'd suggest that they are and the comments are
> superfluous.

I don't think your rule holds water: there are definitely cases where
defines/enums require (or at least are better with) additional comments.
Sentence-long identifier names are not very readable, but sometimes a
sentence of comment can help.

Anyway, I think two of the three are probably unnecessary, if you really
want to ask. The first (EC_PWM_TYPE_GENERIC) seems useful.

But then, how do you suggest handling this in conjunction with your
kerneldoc suggestion? IIRC, kerneldoc requires that if one
entry/field/parameter is documented, then all most be documented. So
avoid kerneldoc on the enum, and just use inline comments?

[snip the rest, which was discussed in other branches of this thread]

Brian